The invention relates to a semiconductor device, in particular a monolithic integrated circuit, having a monocrystalline semiconductor substrate body and an epitaxial layer which is provided thereon on one side and is divided into islands in which at least one circuit element is present, said islands being isolated from the substrate by at least one p-n junction and being separated from one another by an isolation zone which adjoins the isolation on the substrate side.
According to a known construction the epitaxial layer is provided on a substrate body of the opposite conductivity type. The epitaxial layer is divided into islands which are isolated from each other by means of isolation zones of the opposite conductivity type by locally diffusing a suitable impurity from the surface of the epitaxial layer. At the same time, an impurity of the same type which was previously diffused locally in the substrate surface, may diffuse in the epitaxial layer from the substrate. One or more zones may be provided in the island, for example, by diffusion, to form a semiconductor circuit element, for example, a transistor, a diode, a resistor or capacitor. The material of the epitaxial layer remaining after said formation may itself form a component of the circuit element, but in principle it may also serve as an isolation of a circuit element formed in the island. The advantage that such isolation zones can be formed by means of conventional planar techniques and that they can be covered with an oxide layer in normal manner across which layer metal conductors can be conducted, for example, for interconnections of circuit elements in different islands, is offset by the drawback that such an isolation zone has a high doping concentration, particularly at the surface, so that the p-n junction with a juxtaposed island zone has a comparatively low breakdown voltage and high capacity. Moreover, zones of a conductivity type opposite to that of the epitaxially provided material and provided in the island should be separated from the isolation zone by an intermediate zone of the type of the epitaxially provided material, for example, consisting of the epitaxial material itself. Such a separation requires additional space at the surface. When said intermediate zone has a low doping concentration, as will usually be the case, for example, when using the doping in the original epitaxially provided material, there is a possibility that inversion channels are formed at the surface which produce a short-circuiting connection between the isolation zone and a zone present in the island. In order to inhibit such an inversion it is possible to increase the surface concentration of the doping by diffusion but in this case either sharper p-n junctions are formed with proportionally lower breakdown voltage and higher capacity, or more space is required to obtain some distance between said highly doped region and the isolation zone.